Category Archives: SQL Server

You all know that checking our databases for corruption regularly is a must. But what about tempdb? Do you need to check it as well?

The maintenance plans that come with SQL Server do not run DBCC CHECKDB on tempdb, which is a strong indicator that it’s a special database and something different is happening behind the scenes. If you think that relying on the behavior of a poor tool such as maintenance plans to make assumptions on internals is a bit far-fetched, well, I see your point. However, you can get more clues by running DBCC CHECKDB against your tempdb and see what it outputs:
DBCC CHECKDB will not check SQL Server catalog or Service Broker consistency because a database snapshot could not be created or because WITH TABLOCK was specified.

See? Something special is happening here: CHECKDB cannot take a database snapshot to run the consistency checks and has to run as if WITH TABLOCK was specified.

Big deal? It depends. Running CHECKDB WITH TABLOCK means that you revert to the SQL2000 behavior, when table locks were taken to perform the consistency checks. This means that you might impact your workload with blocking. Not good.

Well, tempdb is recreated each time you start the instance and doesn’t contain any data worth worrying about, so you don’t need to check if it got corrupt, right? Again, it depends: tempdb might get so corrupted that it could start to throw errors at the sessions using it. It might also get corrupted to a point that triggers a stop of the instance. Not good.

So, if you check tempdb, you get blocking and if you don’t, you can get errors. What’s a reasonable balance?

Don’t check tempdb in the same schedule you use for checking user databases: find a reasonable maintenance window when any blocking issue is acceptable. Probably once a week is enough.

What should you do if you find corruption in tempdb? Don’t restart the instance right away: it could still survive for some time before problems arise. The whole point of checking tempdb is avoiding unpredicted downtime, so if you cycle the instance as soon as you find corruption, you’re killing the only reason to check it. Plan downtime with your users and cycle the instance when it causes less harm to your business.
Moreover, if something corrupted your tempdb, it has likely corrupted your user databases, so make sure you check everything before shutting down the instance (time to take tail-log backups?).

If your tempdb gets corrupted, restarting the instance won’t be enough to make corruption go away: you will have to stop SQL Server, delete the files manually and the start SQL Server to let it create the new tempdb files.

Even if you don’t mind losing the data stored in tempdb, getting corruption is a sign that something went wrong: make sure you investigate the issue and find the root cause. It could be a problem with the I/O subsystem or a malfunctioning RAM module or something else: fix the root cause before it affects the user databases.

Call to action:

Are you checking your tempdb for corruption? If you are not, don’t panic: choose an appropriate schedule and start checking it.

Pordenone is the place where the Italian adventure with SQLSaturday started, more than two years ago. It was the beginning of a journey that brought many SQLSaturdays to Italy, with our most successful one in Parma last November.

Now we’re back in Pordenone to top that result!

We have a fantastic schedule for this event, with a great speaker lineup and great topics for the sessions. Everything is set in the right direction to be a great day of free learning and fun.

I will have two sessions this time:

SQL Server Security in an Insecure World

In this session I will talk about security, with a general introduction to the topic and then I’ll go straight to demonstrate some of the vulnerabilities that attackers could use to take over your server. Yes, I’ll be demonstrating SQL-Injection attacks: SQL-I is still a top security issue, even if we’re in 2015. Everyone must be aware of the risks and take action immediately.
I will also describe the security features available in SQL Server to lock down the server as much as possible, but the key concept I will try to drive is that security is a process, not a feature.
If you want to find out more, join me at 12:00 PM in room S7.

Extending the Data Collector to Monitor SQL Server effortlessly

In this session I will try to promote one of the least used features in SQL Server: the Data Collector. It doesn’t have all the bells and whistles of the expensive monitoring suites, but it does the job pretty well. Things start to be painfully difficult when you try to extend it with additional collection sets, but the good news is that there’s an open-source project that provides a GUI to manage and customize the collection sets. The project is called ExtendedTSQLCollector and it does much more than just adding a GUI to the Data Collector: it also provides two additional collector types to collect data from LOB columns (in case you’re wondering, no – the vanilla Data Collector doesn’t support LOB columns) and Extended Events sessions.
I will also demonstrate a convenient way to centralize and extend the Data Collector reports to create a reporting and alerting solution for free.
Sounds interesting? Join me at 4:30 PM in room S7.

We’re being told over and over that “throwing hardware at the problem” is not the correct solution for performance problems and a 2x faster server will not make our application twice as fast. Quite true, but there’s one thing that we can do very easily without emptying the piggy bank and won’t hurt for sure: buying more RAM.

The price for server-class RAM has dropped so dramatically that today you can buy a 16 GB module for around € 200. Depending on the architecture of your server, you could max out the memory supported by a standard edition (128 GB) with just € 1,600.

Isn’t it a reasonable price for better performance?

Let’s put it in perspective: you decide that throwing hardware at the problem is not right, so you hire a consultant to tune performance. How many days of his work can you buy with € 1,600? Two? One? How much tuning work will he do in one or two days? Do you want him to work on the core issues or fight with memory pressure? RAM is cheap, consultants are not: make them work on what really matters for you.

Does adding RAM always make sense? No: if your server has 4 GB of data and 16 GB of RAM, there’s no need to add more RAM and if you do you won’t see any improvement. On the other hand, if you have 100 GB of data and 32 GB of RAM, you should be upgrading right away. Isn’t your business worth € 1.600? You’re probably paying much more for SQL Server licensing, so why waste your money on a license that has to run on an underpowered machine? RAM is cheap, SQL Server licenses are not: let your license work on a good machine.

Will it make a huge difference? It depends: if the server is already under heavy memory pressure, you will see a big improvement. Even if memory pressure is not the worst issue on your server, you will see a big difference for those queries that access data not used frequently: if you don’t have enough RAM, that data will probably live outside the buffer cache and will have to be read from disk. RAM is cheap, faster disks are incredibly expensive: let the RAM work and the disks sit idle.

That said, what I see in the wild is lots and lots of production servers with 8 GB of RAM or less. Many of those servers have been installed a few years ago, when RAM was pricier than today, but there’s no reason why you shouldn’t upgrade them now. Upgrading the CPU has an impact on the SQL Server licensing, while adding more RAM doesn’t require additional licensing fees. See? RAM is cheap.

On the other hand, we have many servers running on virtual machines at hosting/cloud facilities, where you pay for machine specs. Something has to change here as well: hosting companies are offering too few RAM in their machines and the configurations with more memory are crazily expensive. Dear hosting/cloud companies, open your eyes: RAM is ridiculously cheap!

Call to action:

Did I mention that RAM is cheap? Check your servers: are they running on less than € 200 of RAM? It’s time to upgrade NOW!

Some weeks ago I blogged about the discouraging signals coming from Connect and my post started a discussion that didn’t go very far. Instead it died quite soon: somebody commented the post and ranted about his Connect experience. I’m blogging again about Connect, but I don’t want to start a personal war against Microsoft: today I want to look at what happened from a new perspective.

What I find disappointing is a different aspect of the reactions from the SQL Server community, which made me think that maybe it’s not only Connect’s fault.

My post was in the headlines of SQL Server Central and was also included in the weekly links that Brent Ozar sends out with the Brent Ozar Unlimited newsletter, so it got a lot of views that day. Looking at my wordpress stats, I see that thousands of people read my post (to be fair, I can only say that they opened the page, I cannot tell whether they read the post or not) and some hundreds of people clicked the link to the original Connect item that started my rant.

Nobody upvoted the item. Yup, nobody.

Ok, very few people love the Data Collector and I rarely see it used in the wild, so, yes: I can understand how nobody cares about a bug in it. But, hey, it’s not my only Connect item that got no love from the community. Here’s another one, involving data corruption when using linked servers. See? Only 9 upvotes.

Here’s another one yet, that involves the setup program. No upvotes except mine.

What’s the point I want to drive? The voting system and the comments are the only way we have to improve the content on Connect. If we disregard the tools we have in our hands, there’s no use in complaining about the feedback system at all.

We need more community engagement

Filing our own items on Connect is not enough: we have to get involved in the platform to make our voice heard in more ways. When we find an item that we’d like to get fixed, we should definitely upvote it. At the same time, when we find items that are poorly described or are related to an issue that can be solved without bothering the support team, we should interact with the OP and ask for clarification or provide an alternative answer. When appropriate, we should also downvote poor questions.

Some popular Q&A sites like StackOverflow have built successful models based on this paradigm, like it or not. Moreover, the “points” system has proved successful at driving user engagement, which is something totally missing from Connect: you file your complaint and never come back.

Some online communities have moderators, who can play a fundamental role in the community. They can flag inappropriate items, edit and format questions and comments. The can also close questions or put them on hold. If part of the problem with Connect is the signal/noise ratio, more power to moderators is a possible answer.

Can PASS help?

In this post, Kevin Kline says that one of the ways that PASS should improve itself could be playing a better role in advocacy, telling Microsoft what are the features we really would like to see in SQL Server vNext and what are the bugs we really need to get fixed in the product. The idea is that Microsoft would (or at least should) listen more attentively to a whole community of users rather than to single individuals.

It’s a great idea and I think that PASS should really go for it. Unfortunately, something like that will never substitute Connect, because it’s a platform to collect feedback for all Microsoft products and not only for SQL Server. Moreover, how PASS is planning to gather the user feedback is still unclear: would it be using a voting system like Connect’s? How would that be different from Connect itself then?

Speed matters

Another thing that I think drives people away from Connect is its dreadful slowness. Connect is slow and nobody uses slow sites. It seems to be getting better lately, but we’re still not there. StackOverflow is probably using a fraction of Microsoft’s hardware and money to run all the StackExchange network at the speed of light. Part of its success is the responsiveness and Connect has a long way to go to catch up.

Bottom line

Connect has its issues, we all know it, but it’s not all Microsoft’s fault. The individual users can do something to improve the quality of the feedback and they definitely should. Everybody can start now! More votes means more attention, less votes means less love. Simple and straightforward.

On the other hand, the communities can contribute too. How they can contribute is not clear yet, but some communities (like PASS) have lots of people that volunteer and make their voice heard. It would really be a shame if that voice got lost.

Microsoft, please do your part. Users and communities want to contribute: help yourself by helping them and you won’t regret it. Responsiveness is the keyword here: we need a more responsive site and more responsive support engineers.

As you probably know, SQL Server allows only one default instance per server. The reason is not actually something special to SQL Server, but it has to do with the way TCP/IP endpoints work.

In fact, a SQL Server default instance is nothing special compared to a named instance: it has a specific instance id (MSSQLSERVER) and listens on a well-known TCP port (1433), but it has no other intrinsic property or feature that makes it different from any other instance.

Let’s look closely to these properties: the instance id is specific to a SQL Server instance and it has to be unique. In this regard, MSSQLSERVER makes no exception. Similarly, a TCP endpoint must be unique and there can be only one socket listening on a specific endpoint.

Nevertheless, I will show you a way to have multiple “default” instances installed on the same server, even if it might look impossible at a first look.

Install two instances of SQL Server

First of all, you need to have two (or more) instances installed on your server. In this example I will use the server “FANGIO” and I will install two named instances: INST01 and INST02.

Here’s what my Configuration Manager looks like once the two instances are ready:

In this case I used two named instances, but it would have worked even if I used a default instance and a named instance. Remember? Default instances are nothing special.

Provision IP addresses

Each SQL Server instance must listen on a different TCP endpoint, but this does not mean that each instance has to listen on a different port: a TCP endpoint is made of an IP address and a port. This means that two instances can listen on the same port, as long as the IP addresses are different.

In this case, you just need to add a new IP address to the server, one for each SQL Server instance that you want to listen on port 1433.

Configure network protocols

Now that you have multiple IP addresses, you just have to tell SQL Server to listen on that specific address, port 1433.

Open the Configuration Manager and enable TCP/IP:

Now open the properties applet and disable “Listen All”:

In the IP Addresses tab, configure the IP address and the port:

In this case I enabled the address 10.0.1.101 for INST01 and I disabled all the remaining addresses. For INST02 I enabled 10.0.1.102.

Configure DNS

Now the server has two IP addresses and they both resolve to its network name (FANGIO). In order to let clients connect to the appropriate SQL Server instance, you need to create two separate “A” records in DNS to resolve to each IP address.

In this case I don’t have a DNS server (it’s my home lab) so I will use the hosts file:

Final Setup

Now the example setup looks like this:

When a client connects to the default instance on ASCARI, it is connecting to FANGIO\INST01 instead. Similarly, the default instance on VILLENEUVE corresponds to FANGIO\INST02.

Why would I want to do this?

If you had only default instances in your servers, moving databases around for maintenances, upgrades or consolidations would be just a matter of adding a CNAME to your DNS.

With named instances, the only way to redirect connections to a different server is by using a SQLClient alias. Unfortunately, aliases are client-side settings and have to be deployed to each and every client in order to work. Group policies can deploy aliases to multiple machines at once, but policies are not evaluated immediately, while a DNS entry can propagate very quickly.

Another reason to use this setup is the ability to bypass the SQLBrowser: when a named instance is specified, the client has to contact the SQLBrowser service on port 1434 with a small UDP datagram and receive back the list of instances, along with the port they’re listening on. When the default instance is specified, there is no need to contact the SQLBrowser, because we already know the port it is listening on (it’s 1433, unless it has been changed).

Some setup guides recommend that you change the port SQL Server listens on to something different from 1433, which is a well-known port, more likely to be discovered by attackers. I think that an attacker skilled enough to penetrate your server needs much more resistance than just “hiding” your instance to a non-default port. A quick port scan would immediately reveal any SQL Server instance listening on any port, so this is really a moot point in my opinion.

Bottom line

SQL Server allows only one default instance to be installed on a machine, but with a few simple steps every instance can be made a “default” instance. The main advantage of such a setup is the ability to redirect client connections to a database instance with a simple change in the DNS configuration.

A couple of years ago I blogged about a bug on the Data Collector that I couldn’t resolve but with an ugly workaround. At the end of that post, I stated that I wouldn’t have bothered filing the bug on Connect, due to prior discouraging results. Well, despite what I wrote there, I took the time to open a bug on Connect (the item can be found here), which was promptly closed as “won’t fix”.

Nothing new under the sun: “won’t fix” is the most likely answer on Connect, no matter how well you document your issue and how easy is the bug to reproduce. I really am sorry to say that, but it’s a widespread feeling that Connect has become totally pointless, if it ever had a point. The common feeling about Connect is that bugs are usually closed as “won’t fix” or “by design” without any further communication, while suggestions are completely disregarded.

How did we get here? Why is Microsoft spending money on a service that generates frustration on users? Where does this idiosyncrasy come from?

If I had to give Microsoft advice on how to improve Connect, I would focus on one simple point:

Improve feedback

One of the things I see over and over on Connect is the lack of communication between users and support engineers. Once the item is closed, it’s closed (with few notable exceptions). You can ask for more information, add details to the item, do anything you can think of, but the engineers will stop responding. Period.

This means that there is no way to steer the engineer’s understanding of the bug: if (s)he read it wrong, (s)he won’t read it again.

I can understand that anybody with a Microsoft account can create bugs on Connect without having to pay for the time spent on the problem by the engineers: this can easily lead to a very low signal/noise rate, which is not sustainable. In other words, the support engineers seem to be flooded by an overwhelming amount of inaccurate submissions, which makes mining for noteworthy bugs an equally overwhelming task.

However, I think that the current workflow for closing bugs is too abrupt and a more reasonable workflow would at least require responding to the first comment received after the item is marked for closure.

How is CSS different?

In this particular case, I decided to conduct a small experiment and I opened the same exact bug with CSS. Needless to say that the outcome was totally different.

The bug was recognized as a bug, but this is not the main point: the biggest difference was the amount and the quality of communication with the support engineer. When you file a bug with CSS, a support engineer is assigned to your case and you can communicate with him/her directly by email. If the engineer needs more information on the case, (s)he will probably call you on the phone and ask for clarification. In our case, we also have a TAM (Technical Account Manager) that gets CC’ed to all emails between us and CSS.

Where does the difference lay? Just one: money.

If you want to contact the CSS, you have to pay for support. If the bug turns out to be a documented behavior instead, you pay for the time spent by the engineers working on it. This is totally absent from Connect, where everyone can file bugs without having to pay attention to what they do: there will be nothing to pay at the end of the day.

Is Connect really pointless?

One thing I discovered with my experiment may surprise you: CSS reads Connect items and if there is one matching your case, they will take it into account. This is really good news in my opinion and sheds a totally new light over Connect.

Another thing I discovered is that there is much more information behind a Connect item than it’s visible to users. When the engineers process items, they produce comments that are attached to the different workflow steps involved in the triage. Unfortunately, this is invisible to the end users, that are left with the minimal information that the engineers decide to share.

However, the important lesson learned from this experiment is that Connect may be frustrating for end users, but it is far from pointless: the information gathered while triaging bugs contributes to the quality of the paid support and, ultimately, to the quality of SQL Server itself. What still is unsatisfactory is the feedback to Connect users, that are getting more and more discouraged to file new items.

An appeal to Microsoft

Dear Microsoft, please, please, please improve the feedback on Connect: more feedback means less frustration for users that submit legitimate and reasonable bugs. Less frustration means more sensible feedback from your users, which in turn helps your CSS and improves the quality of SQL Server. Not everybody can open cases with CSS: this doesn’t mean that they are not contributing positevely to your product (and you know it), so please reward them with a better communication.

Today when I checked my mailbox I found an amazing surprise: I joined the ranks of the Most Valuable Professionals for SQL Server!

I am honoured to join a community of people that I highly respect and have always been my inspiration. The MVPs I had the pleasure to meet are a model to strive for: exceptional technical experts and great community leaders that devote their own time to spread their knowledge. I have never considered myself nearly as good as those exceptional people and receiving this award means that now I have to live up to the overwhelming expectations that it sets.

So, now what?

This award maybe means that I’m on the right track. I will continue to help the community with my contribution, hoping that somebody find it useful in the journey with SQL Server. I will continue to spread whatever I know about SQL Server and all the technologies around it with my blog posts, my articles and my forum answers. I will continue to speak at conferences, SQL Saturdays and technology events around me.

The award opens new possibilities and new ways to contribute and I won’t miss the opportunity to do more!

I am really grateful to those who made it happen, in particular the exceptional people at sqlservercentral.com, where my journey with the SQL Server community began many years ago.

A huge thank you goes also to the Italian #sqlfamily that introduced me to speaking at SQL Server events.

Monitoring blocking and deadlocking hasn’t always been easy. Sometimes, the tools available in SQL Server are not as friendly as we would like them to be.

Some are very useful for alerting, but don’t provide a simple way to capture additional information about the event. For instance, a simple SQLAgent alert for “deadlocks/sec > 0″ is enough to shoot an email to the DBAs whenever a deadlock happens, but it doesn’t provide a simple way to capture the deadlock graph and include it in the email or save it to a destination table.

Some other methods are very useful for capturing all the information we need, but don’t provide a way to fire an alert when the event is captured. For instance, capturing blocked process reports with an Extended Events session is very easy, but firing an alert when the event is captured is not.

In this post I will show you an easy way to combine monitoring and alerting using the cutting edge monitoring technology available in SQL Server: Extended Events.

Extended Events are cool: they can capture events not available otherwise and they impact the monitored server much less than other capture technologies (e.g. SQL Trace). However, as far as alerting is concerned, they are still lacking a piece of the puzzle. In fact Extended Events don’t provide a built-in way to fire an alert whenever an event is captured. With SQL Trace we had Event Notifications that did exactly this, using a Service Broker queue.

It would be great if there was a way to capture events with an XE session, store them to a table for later analysis and alert as soon as the event occurs.

The good news is that a tool that can do that already exists and even better news is that it’s free and open source! Its name is Extended T-SQL Collector.

Extended T-SQL Collector allows you to combine Extended Events and Data Collector, with the addition of alerting for interesting events. All you have to do is download your copy of Extended T-SQL Collector, install it on your server and then set up a collection set for blocking and deadlocking.

If you ever had the chance to play with Data Collector and tried to create a custom collection set, you probably have noticed that it’s not as easy as it should. This part of the Data Collector is missing a Graphical User Interface and requires messing with XML. Nobody likes XML. If you do, be aware that you’re in a very small minority.

Creating the collection set with the GUI

With Extended T-SQL Collector you can create a collection set to capture blocked processes and deadlocks using the GUI.
Here’s how you do it:

1. Start the Collectionset Manager and connect it to your instance.

2. If the custom collector types provided by Extended T-SQL Collector are not installed, install them

3. Right click the “Collection Sets” node and select “Add”

4. Fill the information about your Collection Set and hit “Save”

5. Right click the Collection Set “Blocking and Deadlocking” and select “Add”. Now enter the information for the first collection item (Blocked Processes)

6. Click the “Parameters” button and fill the dialog with the information requested. The most important part of this step is providing a definition for the Extended Events session that captures blocked processes. This is the session I am using:

You also have to enter values for the output table (the name of the table that will hold the data in the MDW database), an optional filter to futher limiting the rows you want to save to the database and the comma separated list of the event session fields you want to add to the destination table. In this case, the filter is “duration <= 40000000" to capture the "blocked_process" event just once, because a new event will be fired each time the configuration option "blocked_process_threshold" and its multiples are exceeded.

7. Now click the “Alerting” tab and enter the information needed to fire an email every time an event is captured. Extended T-SQL Collector uses Database Mail, so make sure you have a profile that you can use for this purpose. Now hit OK to close this dialog and hit “Save” in the main window.

8. Now you need a collection item to collect deadlocks. Right click the collection set on the tree on the left and click “Add”. Now fill the information as you did for the collection item for blocked processes and hit “Save”

9. Hit “Parameters” and provide all the information needed for the collection item. Again, you need a session definition:

Getting Alerts

Now that your session is running, you can be notified via email whenever blocking or deadlocking occurs.

This is a sample of the email you will receive, containing the colums you selected in the setup.

You can also use the Collectionset Manager UI to query the information captured from the MDW database. You just need to right click a collection item and select “Query” from the context menu. Select a table from the dropdown and adjust the date/time range with the sliders:

Does anybody need another good reason to avoid setting AUTO_CLOSE on a database? Looks like I found one.

Some days ago, all of a sudden, a database started to throw errors along the lines of “The log for database MyDatabase is not available”. The instance was an old 2008 R2 Express (don’t get me started on why an Express Edition is in production…) with some small databases.

The log was definitely there and the database looked online. Actually, I was able to query the tables, but every attempt to update the contents ended up with the “log unavailable” error.

Then I opened the ERRORLOG and found something really interesting: lots and lots of entries similar to “Starting up database MyDatabase” over and over… Does it ring a bell?

Some weeks ago I had to wipe my machine and reinstall everything from scratch, SQL Server included.

For some reason that I still don’t understand, SQL Server Management Studio installed fine, but I couldn’t install Books Online from the online help repository. Unfortunately, installing from offline is not an option with SQL Server 2014, because the installation media doesn’t include the Language Reference documentation.

However, I couldn’t get that method to work: the Help Library Manager kept firing errors as soon as I clicked the “Install from Online” link. The error message was “An exception has occurred. See the event log for details.”

Needless to say that the event log had no interesting information to add.

If you are experiencing the same issue, here is a method to install the language reference from disk without downloading the help content from the Help Library Manager: